A ferro-electric capacitor uses ferroelectric material such as, for example, PZT. Ferro-electric devices are typically used in digital electronics by way of ferro-electric RAM (FRAM). FRAM is a random access memory similar to DRAM but uses a ferro-electric layer instead of a dielectric layer to achieve non-volatility. FRAM is thus an alternative non-volatile memory technology that offers the same functionality as Flash memory. FRAM advantages over Flash include: lower power usage, faster write performance and a much greater maximum number (exceeding 1016 for 3.3 V devices) of write-erase cycles.
FRAM also has advantages over DRAM. Specifically, in DRAM, the charge deposited on the capacitor plates leaks across the insulating layer and the control transistor, and disappears. In order for a DRAM to store data for anything other than a short time, e.g., less than one second, every cell must be periodically read and then re-written, a process known as refresh. The refresh operation requires a continuous supply of power.
In contrast, FRAM only requires power when actually reading or writing a cell. As such, FRAM does not require a refresh process. FRAM does work similar to DRAM in write operations, but differently in read operations. Specifically, writing is accomplished by applying a field across the ferro-electric layer by charging the plates on either side of the ferro-electric layer, thereby storing a “1” or “0”. In the read operation, the transistor forces the cell into a particular state, e.g., “0”. If the cell already held a “0”, nothing will happen in the output lines; however, if the cell held a “1”, the re-orientation of the atoms will cause a brief pulse of current in the output. The presence of this pulse means the cell held a “1”. Since this process overwrites the cell, reading FRAM is a destructive process, and requires the cell to be re-written if it was changed.
Currently FRAM cells, though, are not integrated very well into CMOS technologies. Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.